1. Field of the Invention
The present invention relates to an arm structure of a human-type robot, and particularly to an arm structure designed so that when an elbow joint connecting an upper arm portion and a lower arm portion to each other is bent, an object is prevented from being sandwiched between a lower end of the upper arm portion and an upper end of the lower arm portion.
2. Description of the Related Art
There is an animal-type robot capable of walking by four legs, which is known from Japanese Patent Application Laid-open No.2000-218589, wherein each of the four legs is divided into an upper leg portion and a lower leg portion, which are connected to each other by a substantially cylindrical joint, so that they can be bent.
In the above known robot, an axis of the joint is disposed substantially at the center of the width of the upper and lower leg portions as viewed in a direction of the axis of the joint. For this reason, when the upper and lower leg portions are bent into V-shape, there is a possibility that a foreign matter is sandwiched between the upper and lower arm portions in the vicinity of the joint, whereby a smooth operation of the joint may be hindered.
Accordingly, it is an object of the present invention to prevent a foreign matter from being sandwiched between the upper and lower arm portions at a location corresponding to the elbow joint of the human-type robot to hinder the smooth operation of the joint.
To achieve the above object, according to the present invention, there is provided an arm structure of a human-type robot in which an upper arm portion and a lower arm portion are connected to each other by a substantially cylindrical elbow joint so that they can be bent, the upper and lower arm portions having a width larger than the diameter of the elbow joint as viewed in a direction of an axis of the elbow joint, and being bendable in a limited range between an extended position in which they are extended into a substantially straight line and a bent position in which they are bent in one direction from the extended position, wherein the position of the axis of the elbow joint is offset in the one direction from the center of the width of the upper and lower arm portions, and a lower end of the upper arm portion and an upper end of the lower arm portion, which are connected to the elbow joint, are decreased in width toward the elbow joint on a side opposite from the one direction.
With the above arrangement, the position of the axis of the substantially cylindrical elbow joint is offset in the one direction from the center of the width of the upper and lower arm portions (in a direction of bending of the upper and lower arm portions from the extended position to the bent position). Therefore, when the upper and lower arm portions are bent in the one direction from the extended position to the bent position, it is difficult for a gap, into which a foreign matter may enter, to be defined between the upper and lower arm portions in the vicinity of the joint. Thus, it is possible to reliably prevent the foreign matter from being sandwiched between the upper and lower arm portions in the vicinity of the joint. In addition, the widths of the lower end of the upper arm portion and an upper end of the lower arm portion, which are connected to the elbow joint, are decreased toward the elbow joint on the side opposite from the one direction. Therefore, when the upper and lower arm portions are bent in the one direction from the bent position to the extended position, it is difficult for a gap, into which a foreign matter may enter, to be defined between the upper and lower arm portions in the vicinity of the joint. Thus, it is possible to reliably prevent the foreign matter from being sandwiched between the upper and lower arm portions in the vicinity of the joint.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.